As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 1264 AUS-BOS, CREW DECLARED EMERGENCY AND AIR RETURN TO AUS DUE TO AVNX MAU 3A FAILED AFTER TAKEOFF. MAU CB POPPED, QRH PROCEDURE APPLIED. ACCOMPLISHED FIM TASK 31-42-00-810-812A. REMOVED AND REPLACED MAU 3 POWER SUPPLY 1. FAULT CLEARED OPS CHECK OK. CB B34 MAU 3 POWER 1 CB RESET WITH NO FAULTS NOTED.